Fragmentation free radical formation

In this process, the organic halide is split into an ion and a radical fragment. Free-radical formation by oxidation of molybdenum carbonyl with carbon tetrachloride and carbon tetrabromide has been studied in detail [6]. The overall reaction may be represented as follows ... 

A New Mechanism of the Maillard Reaction Involving Sugar Fragmentation and Free Radical Formation... 

Thus we propose the existence of a new pathway to browning in the Maillard reaction, involving sugar fragmentation and free radical formation prior to the Amadori rearrangement. 

M. Namiki and T. Hayashi, A new mechanism of the Maillard reaction involving sugar fragmentation and free radical formation, in B, 1983, 21-46. 

D + Y F S- 6- Semiconductor sensitization of radical formation. A Light absorption and charge trapping by surface adsorbates to give (B) ion radicals. C Free radical formation by ion radical fragmentation. (Adapted from Ref. 17b)... 

The mechanisms of the photooxidation of polyethylene and polypropylene have been discussed in depth with particular emphasis on the importance of hydroperoxides as the precursor to free radical formation . Both the kinetics and nature of the photooxidation products of the polymers are markedly controlled by these species especially polypropylene. On the other hand the density of polyethylene has been found to play an important role on the photooxidation rate of the polymer . Here the photostability of the polymer decreased with decreasing film density indicating that oxygen diffusion is impaired by the crystallites and therefore improves stability. In fact, other workers have found that the crystalline regions of polyethylene are unaffected by irradiation in air . These workers also found new crystalline regions are formed on irradiation due to the smaller polymer fragments... 

Free radicals are molecular fragments having one or more unpaired electrons, usually short-lived (milhseconds) and highly reaclive. They are detectable spectroscopically and some have been isolated. They occur as initiators and intermediates in such basic phenomena as oxidation, combustion, photolysis, and polvmerization. The rate equation of a process in which they are involved is developed on the postulate that each free radical is at equihbrium or its net rate of formation is zero. Several examples of free radical and catalytic mechanisms will be cited, aU possessing nonintegral power law or hyperbohc rate equations. 

A free-radical process consists of at least two steps. The first step involves the formation of free radicals, usually by homolytic cleavage of bond, that is, a cleavage in which each fragment retains one electron ... 

The thermal and photochemical activations of EDA complexes by electron transfer are both enhanced when the radical ions D+- or A--(either paired or free) undergo a facile first-order (unimolecular) transformation such as fragmentation, rearrangement, bond-formation, etc., which pulls the redox equilibrium and thus renders the competition from the energy-wasting back electron transfer less effective (compare Scheme 5). Critical to the quantitative evaluation of the reaction dynamics is the understanding that the typical [D+% A--] intermediates, as described in... 

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